1. Field of the Invention
The present invention relates to a substrate processing apparatus, a focus ring heating method, and a substrate processing method, and in particular to a substrate processing apparatus, a focus ring heating method, and a substrate processing method that control the temperature of a focus ring.
2. Description of the Related Art
In subjecting a wafer as a substrate to plasma processing such as etching, the temperature of the wafer affects the width and depth of grooves formed in a surface of the wafer through etching, and hence it is required to maintain the entire surface of the wafer at a constant temperature during etching.
Substrate processing apparatuses that subject wafers to etching are comprised of a chamber that houses wafers, and a mounting stage on which is mounted a wafer during etching (hereinafter referred to as “the susceptor”). In the chamber, plasma is produced to etch each wafer, and the susceptor has a temperature adjusting mechanism to control the temperature of each wafer. When a wafer is subjected to etching, the wafer is increased in temperature due to exposure to heat from the plasma, and hence the temperature adjusting mechanism of the susceptor cools the wafer so that the wafer is maintained at a constant temperature.
Moreover, in the susceptor, an annular focus ring made of silicon or the like is mounted on the susceptor in such a manner as to surround a peripheral portion of the wafer. The focus ring focuses plasma in the chamber toward the wafer, and the focus ring itself is increased in temperature to, for example, 300 to 400° C. due to exposure to heat from the plasma during etching.
During etching, the most part of the wafer is cooled by the temperature adjusting mechanism of the susceptor, but the peripheral portion of the wafer is affected by radiant heat from the focus ring, and hence it is difficult to maintain the entire surface of the wafer at a uniform temperature. Therefore, it is necessary to control the temperature of the focus ring. It is known that a heater is provided in the focus ring so as to control the temperature of the focus ring (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2005-353812).
Moreover, when a plurality of wafers are subjected to etching one by one by the substrate processing apparatus, changes in focus ring temperature with time have to be made uniform in etching of all the wafers so as to obtain the same etching results with respect to all the wafers.
Meanwhile, since the interior of the chamber is evacuated, a vacuum heat insulation layer is formed at a boundary between the focus ring and the susceptor. Thus, heat cannot be transferred from the focus ring to the susceptor only by mounting the focus ring on the susceptor. For this reason, although the temperature of the focus ring increases to, for example, 300 to 400° C. in etching of each wafer, the initial temperature of the focus ring in etching of the first wafer is low since it had not been exposed to heat before etching, and hence the temperature of the focus ring does not increase to 300° C. Namely, since the initial temperature of the focus ring in etching of the first wafer and the initial temperature of the focus ring in etching of the second and subsequent wafers are different, changes in focus ring temperature with time in etching of the first wafer and changes in focus ring temperature with time in etching of the second and subsequent wafers are different (see FIG. 7A). As a result, the result of etching on the first wafer and the result of etching on the second and subsequent wafers are different.
To cope with this, there has been developed a method in which the heat transfer efficiency between the focus ring and the susceptor is improved, and the focus ring is actively cooled by the temperature adjusting mechanism of the susceptor, so that changes in focus ring temperature with time are made substantially uniform in etching of all the wafers (see FIG. 7B). In this method, to improve the heat transfer efficiency between the focus ring and the susceptor, a heat transfer sheet is interposed between the focus ring and the susceptor, or the focus ring is electrostatically attracted to and held on the susceptor.
However, in the method in which the heat transfer efficiency between the focus ring and the susceptor is improved, the temperature of the focus ring is maintained at a relatively low temperature in etching of each wafer, and hence it is impossible to carry out etching processes or the like that require the focus ring to be at a high temperature, and the kinds of etching processes that can be carried out are limited.
Moreover, in electrostatically attracting and holding the focus ring, direct-current voltage has to be applied to the susceptor during etching, but since radio frequency electrical power is also applied to the susceptor during etching, abnormal electric discharge toward a supply path for the direct-current voltage may occur, and also, the radio frequency electrical power may flow backward to a ground via the supply path for the direct-current voltage.
Further, in the case where the heat transfer sheet is interposed between the focus ring and the susceptor, vacuum heat insulation layers may be respectively formed between the focus ring and the heat transfer sheet and between the transfer sheet and the susceptor, and hence it is difficult to accurately control the temperature of the focus ring.
Of the above described problems, to solve the problem that the kinds of etching processes that can be carried out are limited, methods in which the focus ring is actively heated during etching are being developed. Examples of such methods include a method in which the focus ring is radiated and heated by a lamp or a laser, a method in which a heater is disposed on the surface of the susceptor on which the focus ring is mounted and the focus ring is heated by the heater, and a method in which a heater is provided inside the focus ring as mentioned above.
However, in the case where the focus ring is radiated by a lamp, other component parts as well as the focus ring are heated, and hence it is difficult to accurately control the temperature of the focus ring due to radiant heat from the heated other component parts.
In the case where the focus ring is radiated and heated by a laser, the heating efficiency cannot be stable, and hence it is difficult to accurately control the temperature of the focus ring.
In the case where a heater is disposed on the surface of the susceptor on which the focus ring is mounted, a vacuum heat insulation layer is formed between the focus ring and the heater, and hence it is difficult to accurately control the temperature of the focus ring.
In the case where a heater is provided inside the focus ring, the electrical power has to be supplied to the heater, but since the susceptor and the focus ring have to be connected to each other by wiring, abnormal electric discharge may occur due to the presence of the wiring, and also radio frequency electrical power may flow backward to a ground via the wiring.